Liquid delivery device

ABSTRACT

A fluid delivery device is provided which comprises a microchannel device for cutting out a certain amount of a sample from a micorochannel by controlling a valve opening. The fluid delivery device has a valve for controlling a flow of a fluid, comprising a flow channel for the fluid, and a valve in the flow channel, wherein the valve operates in accordance with a pressure difference between the upstream side and downstream side of the valve caused by the flow of the fluid through the flow channel, allowing the fluid to flow when the pressure difference is lower than a prescribed value P 0 , and intercepting the fluid not to flow when the pressure difference is P 0  or more.

TECHNICAL FIELD

The present invention relates to a liquid delivery device having a valvefor controlling a flow of a fluid, particularly to a liquid deliverydevice having a valve for controlling a flow of a fluid for use in aminiaturized analysis system (μ-TAS: micro total analysis system) forconducting chemical analysis or chemical synthesis on a chip.

BACKGROUND ART

In recent years, with development of microfabrication techniques, thesystems are attracting attention which comprise microchannel,microfluidic devises such as a pump, and a valve, and a sensorintegrated on a substrate like glass or silicon or polymer, and conductchemical analysis on the substrate. Such a system is called a μ-TAS(micro total analysis system), or lab-on-a-chip. The miniaturization ofthe chemical analysis system decreases an ineffective space volume andremarkably decreases the sample amount. The miniaturization enables alsoshortening of the analysis time and decrease of power consumption of theentire system. The miniaturization is promising for lowering the priceof the system. Further, the μ-TAS is promising in medical services suchas home medial care and bed-side monitoring, and biotechnologies such asDNA analysis and proteome analysis.

For the μ-TAS, various types of valves have been disclosed forcontrolling the fluid flow in a microchannel. For instance, a microvalveformed on a silicon substrate by micro-machining is disclosed by M.Esashi, S. Shoji, and A. Nakano: “Normally closed microvalve andmicropump fabricated on a silicon wafer”, Sensors and Actuators, Vol.20,No.1-2, pp. 163-169, 1989. This valve is capable of controlling a fluidflow by driving a diaphragm by a piezoelectric actuator. This documentdiscloses also a one-way valve supporting a driving member elasticallyon a polycrystalline silicon plate. This one-way valve actuates amovable part by action of the flowing fluid itself to close a holeformed in opposition to the driving mechanism to intercept the flowchannel. Such a valve which is driven by the fluid itself without anactuator is called a passive valve. The passive valve employing noactuator is capable of controlling the fluid with a simple structure oflow production cost advantageously.

For the μ-TAS, various types of flowsensors been disclosed forcontrolling a flow of fluid in a microchannel. Japanese PatentApplication Laid-Open No. 2002-355798 discloses a process for computinga flow rate, with a heater formed from an electroconductive thin filmand a temperature sensor in a flow channel, by detecting the temperaturechange corresponding to the flow rate by change of resistivity of theelectroconductive thin film. Such a flowsensor can be incorporated in amicrochannel for measuring a flow rate in a microchannel.

On the other hand, many examples have been reported on utilization ofelectroosmotic flow for cutting out a certain amount of a sample from amicrochannel. In the electroosmotic flow method, a voltage is appliedbetween liquid delivery points to produce a driving force in the entireliquid. This method is suitable especially for delivering microchannelof 100 μm or finer. By utilizing this phenomenon, a sample-cuttingsystem is often employed. For example, in a liquid delivery device 800shown in FIG. 8A, a liquid is allowed to flow by electroosmosis fromreservoir 802 through flow channel 806, intersection 809, and flowchannel 808 to reservoir 804; and then as shown in FIG. 8B, the liquidis allowed to flow from reservoir 801 through flow channel 805,intersection 809, and flow channel 807 to reservoir 803 to cut out theliquid in the portion of intersection 809 to take a certain amount ofsample 810. This sample is delivered to an analysis section.Hereinafter, the certain amount of cut-out sample is defined as a“sample plug”. Nowadays various improvements are being made in shapecontrol of the sample plug, delivery flow channel, and efficiency of thesystem, and so forth.

U.S. Pat. No. 5,900,130 discloses time control of the potential betweenthe electrodes for retardation of spread of a sample in theintercrossing flow channel in liquid introduction and for control of theamount and shape of the sample plug at its formation by.

U.S. Pat. No. 6,153,073 discloses sophistication of combination of theflow channels to introduce two kinds of fluids cyclically into one andthe same analysis section.

In the aforementioned prior art techniques utilizing the electroosmosis,the components of the solute in the sample plug delivered by theelectroosmosis are different in migration rate depending on the mass andelectric charge thereof. Consequently, the components in the sample plugare separated according to the difference in the migration rate, forexample as shown by the numeral 811 in FIG. 8C. The components containedin the solution can be analyzed by outside detector 812. In other words,in this system, the separation of the components begins immediatelyafter formation of the sample plug, and the movement of the sample plugthereafter is not a simple delivery process, but is a part of theanalysis, the system being integration of sample delivery and the sampleanalysis.

DISCLOSURE OF THE INVENTION

Conversely, however, the immediate beginning of the component separationafter sample plug formation makes it impossible to retain the originalcomposition of the sample during the delivery. Therefore, the aboveprocess cannot be utilized in the case where the electrophoreticseparation is undesirable, for instance, in the case where a certainamount of the sample is delivered to outside analysis apparatus.Further, the electroosmosis generates a low driving pressure, being notsuitable for introduction of the sample to an analysis apparatus havinga high flow resistance such as an HPLC column.

In another method, a fluid is delivered by application of a pressure bya pump or the like and the flow channel is controlled by a microvalve tocut out a certain amount of a sample. However, known microvalves requirean external power source such as a piezoelectric element, electrostaticdriving means, and a pressure source, and complicated structure of thedevice. Conventional passive valves, although simple in the structure,can serve only as a one-way valve or a check valve. Therefore, asophisticated system such as the one for delivering a certain amount ofa sample cannot be constituted by using conventional passive valvesonly.

The present invention intends to provide a passive valve forconstituting a complex system, for instance, to deliver a certain amountof a sample. Further the present invention intends to provide a fluiddelivery device comprising a microchannel controlled by opening of avalve for cutting out a certain amount of the sample from themicrochannel.

In a process of measuring a liquid flow rate with a conventionalflowsensor and adjusting a liquid delivery pressure and opening of avalve corresponding to the flow rate, both a flowsensor and a microvalvecapable of active driving are necessary. The conventional flowsensor andthe active-driven microvalve are complicated in the structure, so thatthe provision of both the flowsensor and the microvalve will make largerthe entire system disadvantageously.

The present invention intends also to provide a fluid delivery devicecomprising a passive valve having a simple structure and serving also asa flowsensor.

The present invention provides a fluid delivery device having a valvefor controlling a flow of a fluid, comprising a flow channel for thefluid, and a valve in the flow channel, wherein the valve operates inaccordance with a pressure difference caused by the flow of the fluidthrough the flow channel between the upstream side and downstream sideof the valve, allowing the fluid to flow when the pressure difference islower than a prescribed pressure P₀, and intercepting the fluid flowwhen the pressure difference is P₀ or more.

The present invention provides also a fuel cell having a fuel storingsection for storing a fuel, a power generating section for generatingelectric power by use of the fuel, and a valve provided between the fuelstoring section and the power generating section, wherein the valveoperates in accordance with a pressure difference between the upstreamside and downstream side of the valve caused by flow of the fluidthrough the flow channel, allowing the fluid to flow when the pressuredifference is lower than a prescribed pressure P₀, and intercepting theflow of the fluid when the pressure difference is P₀ or more.

The fluid delivery device of the present invention employs a valve whichis controlled for opening and closing by changing the pressure of thefluid flowing through a flow channel, as a method for cutting out acertain amount of a sample from a microchannel. Therefore, components ofthe fluid can be delivered to an outside analysis apparatus by keepingthe original composition without separation of the fluid componentsduring the delivery. A high pressure is applied for the sample delivery.Therefore, this device is useful particularly as the fluid deliverydevice employing a valve for controlling a flow of a fluid for use in aminiaturized analysis system (μ-TAS) for conducting chemical analysis orchemical synthesis on a chip.

A method for introducing a sample into an analyzing device connectedwith the outside of the liquid delivery device mainly is explained inthe following. A usage of the present invention with the method has anadvantage in that a plurality of analyzing devices can be used byreplacing the connected analyzing device with another analyzing deviceto be connected. The present invention is, however, limited to thisusage. Alternatively, both a region on which the liquid delivery deviceof the present invention is located and a region having the analyzingfunction may be formed on a common TAS chip. This embodiment can reducethe delivery time since the analyzing region is formed in the vicinityof the delivery device. In addition, any connecting portion isunnecessary for the embodiment so that the sample plug hardly loses theshape, to improve the reliability of analysis. Further, the dead volumecan be decreased, which enables small amounts of the buffer solution andthe mobile phase.

The fluid delivery device of the present invention can serve also as aswitch or a flowsensor, realizing a microchannel system for delivery ofa fluid by controlling the flow rate with a simple structure of thedevice. In particular, the fluid delivery device of the presentinvention is useful in a miniature fuel cell which requires a simplestructure of the cell and precise control of the fuel feed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are schematic drawings showing an embodiment of amethod of the present invention for introducing a liquid.

FIGS. 2A, 2B, 2C and 2D are schematic drawings showing anotherembodiment of a method of the present invention for introducing aliquid.

FIGS. 3A and 3B are schematic drawings showing an embodiment of aliquid-controlling element driven by a pressure difference caused byflow of a liquid.

FIGS. 4A, 4B and 4C are schematic drawings showing another embodiment ofa liquid-controlling element driven by a pressure difference caused byflow of a liquid.

FIGS. 5A, 5B and 5C are schematic drawings showing still anotherembodiment of a liquid-controlling element driven by a pressuredifference caused by flow of a liquid.

FIGS. 6A, 6B, 6C, 6D, 6E, 6F and 6G are flow sheets of production of aliquid-controlling element driven by a pressure difference caused byflow of a liquid.

FIGS. 7A and 7B are schematic drawings showing an example of a method ofthe present invention for introducing a liquid.

FIGS. 8A, 8B and 8C are schematic drawings showing a conventional methodfor introducing a liquid.

FIG. 9 is a schematic drawing showing an embodiment of a method of thepresent invention for delivering a liquid.

FIGS. 10A, 10B, 10C, 10D and 10E are schematic drawings showing anembodiment of a liquid delivery device of the present invention.

FIGS. 11A, 11B and 11C are schematic drawings showing a driving processof a fluid delivery device.

FIGS. 12A and 12B are schematic drawings showing a sectional structureof a fuel cell employing a fluid delivery device of the presentinvention.

FIG. 13 is a block diagram showing a constitution of a fuel cellemploying a fluid delivery device of the present invention.

FIG. 14 is an enlarged drawing of a valve portion of a fuel cell of thepresent invention.

FIGS. 15A, 15B and 15C show control steps for controlling the flow ratein a fuel cell employing a fluid delivery device of the presentinvention.

FIG. 16 is a flow chart of a process of controlling a fluid.

FIG. 17 is a flow chart of another process of controlling a fluid.

FIG. 18 is a schematic drawing of an embodiment of a fuel cell employinga liquid delivery device of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are explained below in detail.

(Valve)

FIGS. 3A and 3B show schematically an example of the structure of thevalve of the present invention. FIG. 3A is a plan view, and FIG. 3B is asectional view, respectively of valve 300 of the present invention. Thechannel in the valve is constituted of a region of a small channel 303and a region of large channels 304, 305. The intercepting part is a flatplate 301. This flat plate 301 is supported elastically by spring 302between channels 304 and 305 to be perpendicular to the channel at acertain distance from inlet of channel 303. The diameter of flat plate301 is larger than the diameter of channel 303, whereby flat plate 301will intercept the flow of the fluid when flat plate 301 is displacedtoward channel 303 to reach the boundary between channel 303 and channel305.

FIG. 4A shows flow of the liquid from channel 304 to channel 303 in thisvalve. Such a liquid flow causes pressure drop by flowing throughchannel 305, causing a pressure difference between the surface of flatplate 301 at the side of channel 304 and the surface thereof at the sideof channel 305. This pressure difference drives flat plate 301 towardthe inlet of channel 303.

FIG. 4B shows the state of the valve when pressure difference P₁ causedby the liquid flow from channel 304 to channel 303 is smaller thanthreshold value P₀. Flat plate 301 is displaced by the pressuredifference between the side of channel 304 and the side of channel 305,but will not come to close the inlet of channel 303 owing to therestoring force of spring 302 holding the flat plate. Therefore thefluid flows from channel 304 to channel 303 as shown by arrow 401. Onstopping the delivery of the liquid, flat plate 301 returns to theoriginal position by the righting moment of spring 302.

FIG. 4C shows the state of the valve when pressure difference P₂ causedby the liquid flow from channel 304 to channel 303 is larger thanthreshold value P₀. Flat plate 301 is displaced by the pressuredifference between the side of channel 304 and the side of channel 305to close the inlet of channel 303. Thereby, the flow of the fluid isstopped as shown by arrow 402 at channel 304, and flat plate 301 is keptsealing the inlet of channel 303 by the pressure of the liquid. Onremoving the pressure from the side of the channel 304, flat plate 301comes apart from the inlet of channel 303 by righting moment of spring302 to return to the original position.

From the constitution of this valve, it is clear that the flow fromchannel 303 to channel 304 is not intercepted invariably. Therefore,this valve can also serve as a check valve when used at a pressuredifference caused by the flow from channel 303 to channel 304 largerthan threshold value P₀.

A liquid delivery mechanism, which causes pressure difference caused bya flow of a liquid at the valve, enables constitution of a system forcontrolling a flow of a fluid by controlling the opening and closing ofa valve.

The pressure range for driving the valve depends on a spring constant ofspring 302, the distance between flat plate 301 and channel 303, thediameter of the flat plate 301 and the flow channel 303. The springconstant of spring 302 is a function of the spring length, springthickness, numbers of the spring, and the spring material. A valve whichopens or closes within a required pressure range can be designed byoptimizing the above factors. In a closed state of the valve, flat plate301 is held by the pressure of the fluid to give a high sealing effectwith a high strength.

On stopping the fluid delivery, flat plate 301 returns to the originalposition by the righting moment of the spring. Therefore, the phenomenonof sticking, namely adherence of the flat plate onto the opposingsubstrate by surface tension without returning to original position, isless liable to occur. Such sticking is often a problem in conventionalmicrovalves.

In the case where the above sticking causes no problem, the springconstant may be lower. Thereby the valve can be designed to keep aclosed state without returning flat plate 301 to the original positionby surface tension after stop of the fluid delivery. In such a valve,flat plate 301 can be returned to the original position by applicationof a pressure from the side of channel 303. The same effect can beobtained by shortening the distance between flat plate 301 and channel303, and decreasing the righting moment of the spring in the closedstate.

Spring 302 and flat plate 301 is preferably made from a material whichis resistant to the solution subjected to the analysis and is resistantto some extent to elastic deformation, the material being exemplified bysilicon. A resin like silicone may be used therefor. The surface thereofmay be coated. The material of the substrate for forming the channel isnot limited insofar as it is resistant to the analysis solution, thematerial including glass, silicon, and silicone resins. For employingelectroosmotic flow, a material for producing electroosmotic flow may beused.

By using an intercepting part in a flat plate shape with a gap from theopposing substrate, the fluid pressure drops by passage of a fluidthrough the gap to cause pressure difference between the both sides ofthe intercepting part. This pressure difference moves the interceptingpart toward the substrate.

The shape of the intercepting part is not limited provided that it iscapable of closing the opposing aperture. A circular shape is preferredin view of symmetry of the flow. In particular, to a channel having acircular cross section, a circular flat plate is preferably placed withits center to coincide to that of the channel. Thereby the flow of thefluid and the pressure distribution in channel 305 are made symmetricalto the center axis to stabilize the displacement of the interceptingpart.

The valve of the present invention shown in FIGS. 3A and 3B has flatplate 301 supported by springs 302. In such a valve, flat plate 301 canbe displaced by deformation of the spring only without deformation ofthe flat plate, where the displacement of flat plate 301 is stable, toobtain a stable threshold pressure. It is necessary for deforming onlyspring 302 to design the spring with a small spring constant. Smallthickness and small length in each springs 302 enable the springconstant of the spring to be small. A reduction of the number of springsis also effective in reducing a spring constant of the whole of springs.It is also effective in obtaining a shape little deformative to designflat plate 301 having a great thick.

It is also possible to obtain flat plate 301 and spring 302 both ofwhich are deformed by designing flat plate 301 with a small thicknessand spring 302 with a considerable spring constant. In the case whereboth the flat plate and the spring are deformed, the center of flatplate 301 is deformed into a concave shape, whereby it is possible toclose channel 303 along the outermost portion. As a result, theimprovement of sealing property can be therefore expected.

The shape of the cross-section of spring 302 is not specially limited.The spring may be in a shape of a plate having a rectangularcross-section as shown in FIGS. 3A and 3B, or in a curved shape or azigzag shape. The thickness of the spring may be different from that ofthe flat plate portion.

When a circular flat plate is supported with the center to coincide withthe center of a channel in a channel having circular cross-section, thesupporting positions by springs 302 is preferably symmetrical to thecenter axis. Thereby the pressure distribution in channel 305 is madesymmetrical to the center axis, and the displacement of the flat plateis also made symmetrical thereto, giving a stable threshold pressure,and improving the sealing efficiency in the closed state.

In supporting the flat plate with plural springs, the spring constantsof the respective springs are preferably made equal in view of thestability of displacement of the flat plate.

In the example of the above description, the intercepting portion issupported elastically by flat springs. However, the embodiment of thepresent invention is not limited thereto. For instance, the interceptingpart may be supported elastically at one end by a cantilever, or at bothends by a beam.

(Bypass Line)

A fluid delivery system employing a valve of the present invention isexplained below.

FIG. 9 illustrates a fluid delivery system employing a valve of thepresent invention. This system is constituted of flow channel 901,bypass flow channel 902, flow channel 903, valve 904, and HPLC column905. The flow channel 901 is branched at the downstream end portionthereof into bypass flow channel 902 and flow channel 903. Flow channel903 is connected to HPLC column 905. Valve 904 is provided in bypassflow channel 902. This valve 904 has a constitution similar to that ofthe above-explained valve. In FIG. 9, a flow from left to right isallowed to pass when the pressure difference between the both faces ofthe valve is smaller than P₀, and the flow is intercepted when thepressure difference is not smaller than P₀.

In HPLC analysis, the sample is sometimes pre-treated for washing,concentration, or the like in pretreatment portion at the upstreamportion of the column. In the system shown in FIG. 9, a sample havingbeen treated at a pre-treating section (not shown in the drawing) at theupstream side of flow channel 901 is introduced through flow channel 901and flow channel 903 to HPLC column 905. If an initial portion of thesample introduced from the pre-treating section to flow channel 901contains much contaminant and is not suitable for the analysis, theinitial contaminated portion of the sample is introduced to bypass flowchannel 902 not to deliver it to column 905 to enable accurate analysis.

In delivering a sample from the pre-treatment section to flow channel901, the sample is delivered initially under conditions (introductionpressure, introduction flow rate) to keep the pressure differencebetween the both faces of valve 904 to lower than threshold P₀. In thisdelivery state, valve 904 is kept open. The flow resistance at the sideof flow channel 903 and HPLC column 905 is much greater than flowresistance of bypass flow channel 902. Therefore, the sample which maycontain a contaminant is delivered to the side of bypass flow channel902, not delivered to HPLC column 905.

After lapse of a sufficient time, the sample is delivered under theconditions (introduction pressure, introduction flow rate) to obtain thepressure difference of threshold P₀ or higher between the both faces ofvalve 904. Thereby, valve 904 comes to be closed, and the sample isdelivered through flow channel 903 to HLPC column 905.

As explained above, valve 904 of the present invention is provided inbypass line 902 to control the liquid delivery conditions. Thereby, aportion of the sample delivered from the pre-treatment section but notsuitable for the analysis can be introduced to bypass line 902.

In the above explanation, an HPLC column is taken as an example. Thescope of the present invention is not limited thereto. A system similarto the one of this embodiment is applicable in any fluid elementrequiring a bypass line.

(Introduction of a Certain Amount of Sample)

The fluid delivery device of the present invention is also applicable toa process for introducing a certain amount of a sample in a micro flowsystem. FIGS. 1A, 1B, and 1C show schematically an embodiment of thefluid delivery device of the present invention. The fluid deliverydevice 100 shown in FIG. 1A comprises flow channel 105 corresponding toa first flow channel, flow channel 106 and flow channel 107corresponding to a second flow channel, flow channel 111 correspondingto a third flow channel, and flow channel 110 and flow channel 109corresponding to a fourth flow channel, and injecting intersection 108as an intersection portion of the four flow channels. Valve 112corresponding to a first valve is provided between flow channel 106 andflow channel 107, and valve 113 corresponding to a second valve isprovided between flow channel 109 and flow channel 110. Reservoir 101 isprovided at the end of flow channel 105 at the side opposite tointersection 108, and reservoir 103 is provided at the end of flowchannel 111 at the side opposite to intersection 108. Reservoir 102 isconnected to the end of flow channel 106 at the side opposite to valve112, and reservoir 104 is connected to the end of flow channel 110 atthe side opposite to valve 113.

Reservoirs 101, 102, 103, 104 are respectively related to an electrode(not shown in the drawing). The electrodes are connected respectivelythrough a control means for controlling the voltage of the respectiveelectrodes to power sources (not shown in the drawing). To reservoir101, a pump (not shown in the drawing) is connected to apply a pressureto the flow channel, and reservoir 103 is connected to an outsideanalysis apparatus. Valve 112 is a check valve which allows invariably aflow from channel 106 to flow channel 107 and intercepts a reverse flow.Valve 113 is designed to allow a flow from flow channel 109 to flowchannel 110 at a pressure difference between the both faces of the valvelower than threshold P₀, and to intercept the flow at the pressuredifference of not lower than P₀.

A process of cutting out a certain amount of a sample according to thepresent invention is explained regarding to liquid delivery device 100.

Step A:

In Step A, a first liquid is filled into the first flow channel, thesecond flow channel, the third flow channel, fourth flow channel andintersection portion of the four flow channels.

All of the flow channels and reservoirs in liquid delivery device 100are made ready for use by filling a carrier liquid such as a buffersolution.

Step B:

In Step B, a second liquid is introduced into the second flow channeland the aforementioned intersection portion of the four flow channel,and the fourth flow channel in this order by use of a first liquiddelivery mechanism.

Step B is explained by reference to FIG. 1B. A sample containing ananalysis object material is introduced into reservoir 102. Thepotentials of the respective reservoir are adjusted to allow the sampleto flow along a route from reservoir 102 through flow channel 106, valve112, flow channel 107, injecting intersection 108, flow channel 109,valve 113, and flow channel 110 to reservoir 104. For instance, thepotential at reservoir 102 is made higher than that at reservoir 104 toform the above flow. By bringing the potentials at reservoir 101 andreservoir 103 near to the potential at injecting intersection 108,ooze-out of sample from injecting intersection 108 to flow channel 105or flow channel 111 is prevented. In this embodiment, since pressuredifference P₁ caused in the valve is lower than pressure difference P₀,the threshold for valve closing, valve 113 is kept open in the stepshown in FIG. 1B. Valve 112 is also kept open since the flow is directedfrom flow channel 106 to flow channel 107. In FIG. 1B, the hatchedportion indicates the sample, and arrow 151 indicates the direction ofsample flow.

Step C

In Step C, the second liquid near the cross-section of theaforementioned four flow channels is introduced into the third flowchannel.

Step C is explained by reference to FIG. 1C. To reservoir 101, apressure higher than that of the elecroosmotic flow is applied by apump. Thereby, pressure difference P₂ in the valve becomes higher thanthreshold pressure difference P₀ to intercept the liquid flow from flowchannel 109 to flow channel 110 at valve 113. Valve 112 also interceptsthe liquid flow from flow channel 107 to flow channel 106. Thereby afterapplication of the higher pressure, the flow of the liquid is limited tothe route only from flow channel 105 through injecting intersection 108to flow channel 111. This flow cuts out the fluid in injectingintersection 108 to form sample plug 114 and send it through flowchannel 111 and reservoir 103 to an outside analysis apparatus.

In another embodiment, as shown in FIGS. 2A and 2B, the second flowchannel and the fourth flow channel are shifted laterally to adjust thelength of the injection intersection portion 108 to change the amount ofthe sample plug. Further, as shown in FIGS. 2C and 2D, the first flowchannel and the second flow channel may be exchanged in the position.

In Step C, valve 113 may be designed to allow a small amount of thefluid to flow from flow channel 109 to flow channel 110 without completeinterception, which facilitates cut-out of the fluid in injectingintersection 108 to form stable sample plug 114.

In the above explanation, electroosmosis is employed as the first liquiddelivery mechanism, and a pump is employed as the second liquid deliverymechanism. However, the liquid delivery mechanisms are not limitedthereto. For example, pumps are employed as the first and second liquiddelivery mechanisms, and a certain amount of the sample can be deliveredby controlling the liquid delivery conditions. The pump may becontrolled by controlling pressure and/or flow rate. A pipet may beemployed as the liquid delivery mechanism.

The valve of the present invention is useful in various uses other thandelivery of a certain amount of a sample. Various systems can beconstructed by designing flow channel constitution, valve position,threshold pressures of the valve operation, liquid delivery conditions(pump delivery conditions, switching of electrodes for electroosmosisgeneration, etc.) in correspondence with an intended system.

(Fluid Delivery Device for Controlling Pressure-Generating Means forLiquid Delivery by Detection of Flow Rate)

The fluid delivery device of the present invention is useful also fordelivery of a fluid by controlling the flow rate. FIG. 10A shows anembodiment of the fluid delivery device of the present inventionemployed for control of a flow rate. FIG. 10B is a sectional view takenalong line 10B-10B. FIG. 10C is a sectional view taken along line10C-10C. In FIG. 10A, fluid delivery device 1001 has movable flat plate301 which is operated by a pressure difference caused by a flow of afluid between the upstream side and downstream side of the valve, firstelectrode (movable electrode) 1002 placed on the flat plate, valve sheet1004, and second electrode (immovable electrode) 1003 placed on thevalve sheet. Here, the “valve sheet” signifies the contact portion whichcomes to be in contact with flat plate 301 to intercept the channel 303without the electrode. The first electrode and the second electrode mayhave respectively an insulating film thereon. A pump (not shown in thedrawing) is connected to the upstream side of the fluid delivery devicefor delivering the fluid. First electrode 1002 and second electrode 1003are connected (not shown in the drawing) to a detecting means fordetecting the electrostatic capacity between the electrodes. The flow ofthe fluid is controlled by the electrostatic capacity detected by thedetecting means.

The method for detecting the flow rate with the fluid delivery device ofthe present invention is explained below.

The electrostatic capacity produced between the first electrode and thesecond electrode is defined by the formula below:C=εS/d   [Formula 1]where C is the electrostatic capacity, ε is the dielectric constant ofthe fluid, S is the area of the electrode, and d is the distance betweenthe electrodes.

The electrostatic capacity at the initial state as shown in FIG. 10D isdefined to be C₀ according to Formula 1. A flow of the fluid fromchannel 304 to channel 303 causes a pressure difference between theupstream side and the downstream side of flat plate 301 to move firstelectrode 1002 toward valve sheet 1004 as shown in FIG. 10E. Thereby,the distance between the electrode is shortened to change theelectrostatic capacity from C₀ to C₁ (C₁>C₀). The movement position ofthe flat plate depends on the flow rate. Therefore the flow rate can becalculated from measurement of the electrostatic capacity between theelectrodes. Incidentally, in FIGS. 10B and 10C, the numeral 1005 denotesa lead-out wiring.

A process for controlling the flow rate by the fluid delivery device ofthe present invention is explained by reference to the flow chart inFIG. 16. In FIG. 16., the flow controlling process is surrounded byframe line 1601.

Firstly, a fluid is introduced (S61). Then the electrostatic capacityproduced between the electrodes is measured (S62). The flow rate of theflow through the fluid delivery device of the present invention isderived from the measured electrostatic capacity (S63). Then judgment ismade whether the derived flow rate is higher or lower than apredetermined reference flow rate (S64). When the flow rate is equal tothe reference flow rate, the fluid is discharged outside (S65). When theflow rate is lower than the reference flow rate, command is given to thepump to increase the pressure (S66), whereas, when the flow rate ishigher than the reference flow rate, command is given to the pump tolower the pressure (S67). By repeating the above steps, the fluid in thefine fluid system is controlled at an intended flow rate.

In the above example, a pump is used as the pressure generating meansfor delivery of the fluid, but is not limited thereto in the presentinvention. For instance, a heater is provided in the channel to heat thefluid and to deliver the fluid by utilizing the pressure of the gas,wherein the delivery flow rate can be controlled by controlling theheating conditions.

(Fluid Delivery Device for Controlling Pressure-Generating Means forLiquid Delivery in Accordance with Intended Flow Rate)

The fluid delivery device of the present invention is useful in deliveryof a fluid by controlling a switch of external circuit for controllingthe microchannel system in accordance with an intended delivery flowrate. In this case, the flow of the fluid is controlled by detecting thecontact of first electrode (movable electrode) 1002 attached to flatplate 301 with second electrode (fixed electrode) 1003 attached to valvesheet 1004.

The process of controlling the flow rate in this embodiment is explainedbelow by reference to FIGS. 11A, 11B, and 11C. FIG. 17 is a flow chartof this control process. In FIG. 17, the flow controlling process issurrounded by frame line 1701.

In the initial state in which the fluid is not flowing as shown in FIG.11A, the electrodes keeps a predetermined distance and are not incontact with each other. With the flow of fluid from channel 304 tochannel 303 (S71), a pressure difference is caused between the upstreamside and downstream side of flat plate 301 to displace first electrode1102 toward valve sheet 1004, and the fluid pressure difference isjudged (S72). When the pressure difference caused by the fluid flow isless than the threshold pressure for closing the valve, the electrodesare not brought into contact as shown in FIG. 11B. With the electrodenot in contact, a command is given to the pump to generate a pressure(S73), and the fluid is discharged outside (S74). When the pressuredifference is larger than the threshold pressure for closing the valve,first electrode 1102 is bought into contact with second electrode 1103as shown in FIG. 11C, and the contact is detected by an externalcircuit, and a command is given to the pump to stop generation of thepressure (S75), whereas when the pressure difference is smaller than thethreshold pressure for closing the valve, the valve is opened by therighting moment of spring 302. In this open state in which firstelectrode 1102 and second electrode 1103 are not in contact, a commandis given to the pump to generate a pressure. Thus the flow rate iscontrolled in the fine fluid system at an intended level by repeatingthe above steps. In FIGS. 11B and 11C, the blank arrow mark shows arelative flow rate of the fluid schematically.

In the above example, a pump is used as the pressure generating meansfor delivery of the fluid, but is not limited thereto in the presentinvention. For instance, a heater is provided in the channel to heat thefluid and to deliver the fluid by utilizing the pressure of the gas,wherein the delivery flow rate can be controlled by controlling theheating conditions.

Next, a device for controlling fuel feed in a fuel cell by use of thefluid delivery device of the present invention will be described. A fuelcell employing the fluid delivery device of the present invention isexplained.

FIG. 12A is a plan view of the fuel cell. FIG. 12B is a front view ofthe fuel cell. FIG. 13 shows outline of the system of the fuel cell.FIG. 14 is an enlarged drawing of a microvalve shown in FIGS. 12A and12B. The fuel cell has an external size of 50 mm×30 mm×10 mm, which isnearly the same size as the size of the lithium ion battery of anordinary compact camera.

As shown in FIGS. 12A and 12B, the fuel cell has air holes 1301 on theupper face, the bottom face, and the side faces for taking in oxygenfrom outside air as an oxidant for the reaction. These air holes 1301serve also to release formed water as water vapor and release the heatof the reaction to the outside. The fuel cell has also electrodes 1302for taking out the electric power, and fuel charging hole 1303. As shownin FIG. 13, the fuel cell is constituted of polymer electrolyte film1501, oxidizer electrode 1502 of the cell electrode, fuel electrode1503, fuel battery cell (power generation section) 1306, fuel tank (fuelstorage section) 1304, and fuel feeding section 1404 which connects thefuel tank and fuel electrodes of cells and has a valve for controllingthe flow rate of the fuel. Further as shown in FIG. 14, the fuel feedingsection is constituted of fuel electrode chamber 1601 for feeding thefuel to the fuel electrodes, oxidizer electrode chamber 1502 for feedingan oxidizer to the oxidizer electrode, and microvalve 1305 forcontrolling the fuel channel for fuel feed.

Fuel tank 1304 is filled a hydrogen-occluding metal which is capable ofoccluding hydrogen. The hydrogen-occuluding metal is exemplified byLaNi₅. The fuel tank occupies a half the volume of the entire fuel cell.The wall thickness of the tank is 1 mm. The construction material of thetank is titanium. The stored hydrogen is fed to the power generatingcell by heating the hydrogen-occluding alloy.

The power generation process of the fuel cell is explained by referenceto FIG. 13. The hydrogen is fed from fuel tank 1304 throughfuel-supplying section 1404 to fuel electrode 1503. Arrow 1351 shows thehydrogen feed direction schematically. On the other hand, oxygen is fedfrom the outside through air hole 1301 to oxidizer electrode 1502. Arrow1352 shows the air feed direction schematically. Thereby,electrochemical reaction occurs on the surface of polymer electrolytefilm 1501 to generate electric power in the fuel cell. The generatedelectric power is supplied from electrode 1302 to a small electricappliance 1360. Arrow 1353 shows the supply direction of the generatedelectric power.

Next, the opening-closing operation of the valve for power generation ofthe fuel cell is explained by reference to FIGS. 15A, 15B, and 15C.During the shutdown, hydrogen is not fed from the fuel tank since thehydrogen in the fuel electrode chamber 1601 is not consumed. In thisstate, the valve is in an open state (FIG. 15A). On starting the powergeneration, the fuel in the fuel cell chamber is consumed, and thepressure of the fuel in the fuel electrode chamber decreases. Thushydrogen is fed from the fuel tank through the valve, whereby the flatplate is moved toward the valve sheet side (FIG. 15B). On stopping thepower generation, hydrogen consumption is stopped with the hydrogenremaining unconsumed in the fuel electrode chamber, and fuel feed comesto be stopped. Thereby, the flat plate comes to be in an open state(FIG. 15A).

Next, a function of the valve of the present invention as a stop valvefor protecting the power generating cell is explained below.

(Function of Protection of Power-Generating Cell During Filling ofHydrogen to Fuel Tank)

For a sufficient amount of hydrogen occlusion in the fuel tank, thepressure in the fuel tank needs to be raised up to several atmospheres.On the other hand, the pressure at the power-generating cell side isabout one atmosphere for utilizing the outside air. Therefore, an abruptflow of the hydrogen from the fuel cell to the power-generating cellshould be prevented for protection from damage of the interior of thepower-generating cell.

The liquid delivery device of the present invention is provided betweenthe fuel tank and the power-generating cell, whereby the valve of thepresent invention performs a function of preventing abrupt hydrogeninflow into the power-generating cell during hydrogen filling into thefuel tank.

An excessive hydrogen inflow into the fuel feeding section closes thevalve as shown in FIG. 15C to prevent abrupt inflow of the hydrogen intothe power-generating cell and to protect the power-generating cell. Thearrow 1551 shows the inflow of hydrogen from the fuel tankschematically.

The occlusion of hydrogen by the hydrogen occlusion alloy lowers thepressure in the fuel tank, decreasing the pressure difference betweenthe fuel tank side and the power-generating cell side to be lower thanthe threshold pressure. Thereby the valve is opened by the rightingmoment of the spring, and the hydrogen comes to be fed to thepower-generating cell (FIG. 15B).

As explained above, the fluid delivery device of the present inventionserves as a stop valve for protecting the power-generating cell duringfilling of hydrogen to the fuel tank. The device begins fusel feedautomatically with decrease of the pressure in the fuel tank.

(Function of Protecting Power-Generating Cell During Power Generation)

To a fuel cell, necessary hydrogen is fed by heating a hydrogenocclusion alloy by a heater. The interior of the power generating cellshould be protected from damage by abrupt hydrogen supply to thepower-generating cell by excessive temperature rise by malfunction ofthe heater.

The fluid delivery device of the present invention, which is placedbetween the fuel tank and the power-generating cell, performs a functionof preventing abrupt inflow of hydrogen into the power-generating cellduring power generation. When excessive hydrogen is introduced into thefuel feeding section by malfunction of the heater in the fuel tank, thevalve of the present invention is capable of serving as a stop valve tostop the hydrogen feed.

Further, the fluid delivery device as shown in FIGS. 10A to 10E of thepresent invention, when used in the fuel cell, is capable of controllingthe fuel flow by detecting the opening state of the valve. The controlof the fuel flowing through the fluid delivery device can be conductedby detecting the electrostatic capacity between the electrodes.Therefore, the fluid delivery device of the present invention iseffective in flow rate control in the fuel cell.

A fuel delivery control system can be realized by employing the fluiddelivery device of the present invention.

The fuel control is conducted by detecting the electrostatic capacity atfixed time intervals to decrease the power consumption. Therefore, thepresent invention is useful especially for a miniature fuel cell inwhich the fuel is controlled precisely with a simple structure.

(Function for Detecting Operation State of Stop Valve)

During a hydrogen-filling operation, the valve should be closed forprotection of the power-generating cell. The closed state of the valvecan be detected by use of the fluid delivery device of the presentinvention. The normal functioning state of the stop valve can bedetected by the fluid delivery device of the present invention. Forinstance, when the valve is not normally functioning owing to damage orother cause, the contact between the electrodes is not detected. In sucha case, an alarm sound may be generated to inform the user about thedisorder of the stop valve and danger of hydrogen leakage.

(Function of Detecting Completion of Hydrogen Filling Into Fuel Tank)

The fluid delivery device is useful for detecting the completion ofhydrogen filling into the fuel tank. The hydrogen filled in the fueltank is to be fed by opening the valve to the power-generating cell. Theopening state of the valve can be detected by utilizing the switchingfunction of the fluid delivery device of the present invention.

After completion of the hydrogen filling, the pressure in the fuel tankbecomes lower. Thereby the pressure difference between the upstream sideand downstream side of the valve decreases to be lower than thethreshold pressure for valve closure. The decrease of the pressuredifference results in opening of the valve to feed the hydrogen to thepower-generating cell. The completion of the hydrogen filling can beknown by detecting the detachment of the contacting electrodes.

The present invention is explained below in detail by reference toExamples. In Examples, dimensions, shapes, materials, and productionprocess conditions mentioned are merely for illustration, and may bechanged as design items within the range satisfying the requirement ofthe present invention.

EXAMPLE 1

In this Example, a liquid delivery device is practically produced whichhas valves controlled by pressure change of the fluid.

FIGS. 5A, 5B, and 5C show a specific example of production of the fluiddelivery device shown in FIGS. 1A, 1B, and 1C. The fluid delivery deviceis constituted of substrates 500, 501, 502, 503, and 504 as shown inFIG. 5B. FIG. 5A is a plan view of substrate 500 in which channels shownin FIGS. 1A to 1C are formed. FIG. 5B is a sectional view taken alongline 5B-5B in FIG. 5A. FIG. 5C is a plan view taken along line 5C-5C inFIG. 5A.

FIG. 5B shows specifically the route of fluid flow from flow channel 109through the valve and flow channel 110 to reservoir 104. The fluidhaving passed through flow channel 109 in substrate 500 is injected viathrough-hole 505 in substrate 504 into large channel region 304 insubstrate 503. Flat plate 301 provided in substrate 503 is displaceddepending on the fluid pressure and the spring constant of spring 302.When the displaced flat plate 301 shuts the inlet of region 303 having asmall channel in substrate 502, the fluid is stopped in large channelregion 304 in substrate 502, not to flow into channel 303. On the otherhand, when the displaced flat plate 301 does not shut the inlet tochannel 303, the fluid passes through channels 305 and 303 to channel506 in substrate 501, and thereafter the fluid passes via through hole507 in substrate 502, through-hole 508 in substrate 503, andthrough-hole 509 in substrate 504 into flow channel 110 on substrate500, and is discharged out of the system via reservoir 104.

The dimensions of parts of the device are exemplified below. Substrates500, 501 have a thickness of 200 to 500 μm. Substrates 502, 504 have athickness of 200 μm. The channels formed in substrates 500, 501 have abreadth of 100 μm and a depth of 20 to 100 μm. Substrate 503 is an SOIsubstrate having thicknesses silicon/silicon oxide film/silicon of 5μm/0.5 μm/200 to 500 μm. Through-holes 303, 505, 507, 508, 509 formed onsubstrates 502, 503, 504 have diameter of 100 μm. Regions 304, 305 of alarge channel have a diameter of 300 μm. The valve-forming flat plate301 has a diameter of 200 μm, and a thickness of 5 μm. Spring 302 has alength of 50 μm, a thickness of 5 μm, and a breadth of 20 to 40 μm. Thelength of channel 305, namely the distance between non-displaced flatplate 301 and through-hole 303, is 5 μm. The respective reservoirs insubstrate 504 have a diameter of 1 mm.

A process for producing the valve of this Example is explained below.FIGS. 6A to 6G illustrate the process for producing substrate 503,viewed at cross section corresponding to cross section B-B′ in FIG. 5A.

Firstly, on SOI substrate 600, on the side of 5 μm-thick silicon, apattern of a valve comprising flat plate 301 and spring 302 shown FIG.3A and through-hole 508 are formed by photolithography by use ofphotoresist 601 (FIG. 6A).

Next, SOI substrate 600 is dry-etched by SF₆-C₄F₈ gas plasma by use ofphotoresist 601 as the etching mask to form flat plate 301 of depth of 5μm, spring 302, and a part of through-hole 508 (FIG. 6B) by utilizingthe silicon oxide layer as the etching stopper.

Thereafter, the photoresist is removed by O₂ plasma treatment. Thesubstrate is washed by a mixture of a sulfuric acid solution and anaqueous hydrogen peroxide solution at a temperature of 110° C. (FIG.6C).

On SOI substrate 600 on the side of the silicon of thickness of 200 to500 μm, a pattern of a part of channel 304 and a part of through-hole508 by photolithography by using photoresist 602 (FIG. 6D).

SOI substrate 600 is dry-etched by SF₆—C₄F₈ gas plasma by use ofphotoresist 602 as the etching mask to reach and bare the silicon oxidefilm as the etching stopper to form a part of channel 304 and a part ofthrough-hole 508 (FIG. 6E).

The bared portion of the silicon oxide film of SOI substrate 600 isdry-etched by a CF type gas plasma by using photoresist 602 as theetching mask to form channel 304 and through-hole 508 (FIG. 6F).

Finally, the photoresist is removed by O₂-plasma treatment, and thesubstrate is washed with a mixture solution of sulfuric acid and aqueoushydrogen peroxide at 110° C. (FIG. 6G).

The structure of substrate 503 is finished through the above steps.

As substrates 500 and 501, glass plates are patterned to form channelsby photolithography and wet etching by HF. As substrate 502, silicon isused, and the silicon is treated by combination of photolithography andSF₆—C₄F₈ gas plasma dry-etching in a similar manner as substrate 503. Assubstrate 504, glass is used, and the glass is sand-blasted to formthrough-holes.

Substrates 500, 501, 502, 503, and 504 are bonded by thermal fusion (notshown in the drawing).

EXAMPLE 2

With the device prepared above as shown in FIGS. 5A, 5B, and 5C, a unitfor separation and analysis is constructed for analysis of a mixturesolution containing benzoic acid, salicylic acid, and phenol by HPLC(high performance liquid chromatography). FIGS. 7A and 7B illustrate theunit schematically.

Unit 700 is constructed on a substrate, having first channel 710, secondchannel 703-704, third channel 711, fourth channel 706-707, injectingintersection 705, valve 708 in channel 703-704, and valve 709 in channel706-707. Reservoir 701 is connected to the end of flow channel 703 atthe side opposite to valve 708, and reservoir 702 is connected to theend of flow channel 707 at the side opposite to valve 709. Flow channel710 is connected to pump 712 and flow controller 713 at the outside ofunit 700 at the channel end opposite to intersection 705 for injection.Flow channel 711 is connected to an outside analysis apparatus, HPLCcolumn 714, at the channel end opposite to injecting intersection 705.

Valves 708 and 709 are respectively a liquid differential-pressuredriven type of valve shown FIG. 5B. Flow channels 109 and 110 in FIG. 5Bcorrespond respectively to flow channels 704 and 703 of valve 708, andto flow channels 706 and 707 of valve 709. An electrode is connected(not shown in the drawing) to each of reservoirs 701 and 702 to controlmovement of the fluid by electroosmosis.

The analysis object sample solution is an aqueous mixture solution ofbenzoic acid, salicylic acid, and phenol in 100-mM phosphate buffersolution (pH=7.0; KH₂PO₄—Na₂HPO₄). The mobile phase solution is amixture of the above phosphate buffer solution and methanol (mixingratio 75:25).

The process of analysis is shown below. Firstly, the inside of the flowchannel in the unit 700 is entirely filled with the mobile phasesolution (not shown in the drawing). An analysis object sample solutionis introduced from reservoir 701, and is delivered, as shown in FIG. 7A,by electroosmosis through flow channel 703, valve 708, flow channel 704,injecting intersection 705, flow channel 706, valve 709, and flowchannel 707 to reservoir 702. For the delivery, the potential ofreservoir 701 is set at 5 kV, and reservoir 702 is grounded. In the stepof FIG. 7A, valve 708 and valve 709 are kept open.

Then as shown in FIG. 7B, a pressure exceeding the electroosmotic flowis applied to flow channel 710 by pump 712. This applied pressure closesvalve 708 and valve 709, and cuts out the solution in the portion ofinjecting intersection 705 as sample plug 715 to move it by the pressedflow through flow channel 711 and introduces it into HPLC column 714 ofan outside analysis apparatus. The pressure applied by the pump is 0.1to 0.3 MPa.

This HPLC column 714 is a reversed phase chromatographic columnemploying an ODS (octadecylated silica). The separated components aredetected respectively by a UV absorption detector at a UV wavelength of280 nm. As the result, three distinct output signal peaks are obtainedaccording to the elution times of benzoic acid, salicylic acid, andphenol.

As described above, a system can be constructed which cuts out anintended amount of a sample and delivers it by a pressed stream bycombination of an electroosmotic flow and a pressure driven flow tocontrol the flow of a solution. In particular, the present invention isuseful in HPLC which requires high pressure much higher thanelectroosmotic pressure for sample injection.

EXAMPLE 3

With the device for analysis of FIGS. 5A, 5B, and 5C, an HPLC apparatusis constructed for separation and analysis of five kinds of proteins ina solution including glutamate dehydrogenase, lactate dehydrogenase,enolase, adenylate kinase, and cytochrome c. FIGS. 7A and 7B show thedevice schematically.

Unit 700 is constructed on a substrate, having first channel 710, secondchannel 703-704, third channel 711, fourth channel 706-707, injectingintersection 705, valve 708 in channel 703-704, valve 709 in channel706-707. Reservoir 701 is connected to the end of flow channel 703 atthe side opposite to valve 708, and reservoir 702 is connected to theend of flow channel 707 at the side opposite to valve 709. Flow channel710 is connected to pump 712 and flow controller 713 at the outside ofunit 700 at the channel end opposite to intersection 705 for injection.Flow channel 711 is connected to an outside analysis apparatus, HPLCcolumn 714, at the channel end opposite to injecting intersection 705.

Valves 708 and 709 are respectively a liquid differential-pressuredriven type of valve shown FIG. 5B. Flow channels 109 and 110 in FIG. 5Bcorrespond respectively to flow channels 704 and 703 of valve 708, andto flow channels 706 and 707 of valve 709. An electrode is connected(not shown in the drawing) to each of reservoirs 701 and 702 to controlmovement of the fluid by electroosmosis.

The analysis object sample solution is an aqueous mixture solutioncontaining the aforementioned five proteins in a 50 mM phosphate buffersolution (pH=7.0) containing 0.3M NaCl (final concentration of eachprotein being 1.5 mg/mL). The mobile phase solution is a mixture of theabove phosphate buffer solution and methanol (mixing ratio 75:25).

The process of analysis is shown below. Firstly, the inside of the flowchannel in the unit 700 is entirely filled with the mobile phasesolution (not shown in the drawing). An analysis object sample solutionis introduced from reservoir 701, and is delivered, as shown in FIG. 7A,by electroosmosis through flow channel 703, valve 708, flow channel 704,injecting intersection 705, flow channel 706, valve 709, and flowchannel 707 to reservoir 702. For the delivery, the potential ofreservoir 701 is set at 5 kV, and reservoir 702 is grounded. In the stepof FIG. 7A, valve 708 and valve 709 are kept open.

Then as shown in FIG. 7B, a pressure exceeding the electroosmotic flowis applied to flow channel 710 by pump 712. This applied pressure closesvalve 708 and valve 709, and cuts out the solution at the portion ofinjecting intersection 705 as sample plug 715 to move it by the pressedflow through flow channel 711 and introduces it into HPLC column 714 ofan outside analysis apparatus. The pressure applied by the pump is 0.1to 0.3 MPa.

This HPLC column 714 is of a silica type GFC (size separation) mode. Theseparated proteins are detected respectively by a UV absorption detectorat a UV wavelength of 280 nm. As the result, five distinct output signalpeaks of glutamate dehydrogenase, lactate dehydrogenase, enolase,adenylate kinase, and cytochrome c are obtained according to the elutiontimes relating to the molecular weights.

As described above, a system can be constructed which cuts out anintended amount of a sample and delivers it by a pressed stream bycombination of an electroosmotic flow and a pressed flow to control theflow of a solution. In particular, the present invention is useful inHPLC which requires high pressure much higher than electroosmoticpressure for sample injection.

EXAMPLE 4

In this Example, a flow rate of a fluid is controlled according to anelectrostatic capacity with the fluid delivery device shown in FIGS. 10Ato 10E.

The fluid delivery device in FIGS. 10A to 10E.

The fluid delivery device in FIGS. 10A to 10E is employed in a fuel cellmounted on a digital camera. The fluid delivery device is placed in thechannel between a fuel storing section and a power generating section.FIG. 18 is an enlarged drawing of the valve connected to the fuel cell.In the fluid delivery device of FIG. 18, first electrode 1801 isprovided on flat plate 301, and second electrode 1802 is provided onvalve sheet 1004. An insulating film (not shown in the drawing) may beprovided on the first electrode and/or the second electrode. An externalcircuit (not shown in the drawing) is connected to the first electrodeand the second electrode for detecting the electrostatic capacitybetween the electrodes. The material for the electrodes is aluminum. Thematerial for the insulating film is a silicon oxide film. The hydrogenocclusion alloy in the fuel tank is LaNi₅. The digital camera consumesan electric power of 7 W. For producing this power, the hydrogen is fedat a flow rate of 50 mL/min. Therefore, in this device, the normalfeeding rate is set at 50 mL/min.

The process of delivering the fuel by controlling the fuel flow rate isexplained below.

On receiving a command for power generation, the fuel is delivered fromthe fuel tank to the fuel electrode. In this step, the hydrogen flowrate is found to be 20 mL/min by electrostatic capacity measurementbeing lower than the normal flow rate of 50 mL/min. Therefore, heatingof LaNi₅ is started. The heating increases the hydrogen dissociationpressure of LaNi₅ to increase the hydrogen delivery pressure. Thehydrogen flow rate is found to be 70 mL/min by electrostatic capacitymeasurement. Since the measured flow rate is higher than the normal flowrate, LaNi₅ is cooled to lower the hydrogen dissociation pressure ofLaNi₅ to lower the hydrogen delivery pressure. Thereby, the deliveryrate of the hydrogen is found to be 50 mL/min according to electrostaticcapacity measurement.

By repeating the above steps, the normal flow rate of 50 mL/min can bemaintained precisely. As the result, the fuel cell generates the powerof 7 W, enabling stable use of the digital camera.

As described above, the flow rate of the hydrogen through the valve canbe controlled at a prescribed level by controlling the hydrogenproducing pressure according to the hydrogen flow rate measurement. Inparticular, in miniature fuel cells, the fuel should be precisely fedwith a simple structure. This Example shows the effectiveness of thepresent invention.

EXAMPLE 5

In this Example, the feed of a fuel is controlled by detecting anopening state of a valve with the fluid delivery device shown in FIGS.10A to 10E.

The fluid delivery device in FIGS. 10A to 10E is employed in a fuel cellmounted on a digital camera. The fluid delivery device is placed in thechannel between a fuel storing section and a power generating section.FIG. 18 is an enlarged drawing of the valve connected to the fuel cell.In the fluid delivery device of FIG. 18, first electrode 1801 isprovided on flat plate 301, and second electrode 1802 is provided onvalve sheet 1004. An external circuit (not shown in the drawing) isconnected to the first electrode and the second electrode for detectingthe contact between the electrodes. The material for the electrodes isaluminum. The hydrogen occlusion alloy in the fuel tank is LaNi₅. Thesmall electronic unit consumes an electric power of 7 W. For producingthis power, the hydrogen is fed at a flow rate of 50 mL/min. The valveis designed to close when the hydrogen flow rate reaches 100 mL/min.

The process of delivering the fuel by controlling the opening of thevalve by detecting the opening state of the valve is explained below.

On receiving a command for power generation, hydrogen is delivered fromthe fuel tank to the fuel electrode. The flow of hydrogen through thevalve displaces flat plate 301 toward valve sheet 1004. After detectionof the opening state of the valve, heating of LaNi₅ is started. Therebythe hydrogen dissociation pressure of LaNi₅ increases to increase thehydrogen delivery pressure. Next, assuming occurrence of malfunction ofthe heater, the fuel storage section is forcibly heated from outside.Thereby the hydrogen dissociation pressure rises to increase thehydrogen delivery pressure. This increases the hydrogen flow rate in thevalve to 100 mL/min or more, and closes the valve. The resulting contactbetween the electrodes is detected by the external circuit, which stopsthe heating of LaNi₅. As the results, the hydrogen dissociation pressurebecomes lower; hydrogen delivery pressure is lowered; the pressuredifference between the fuel storage section side and the powergeneration section side of the valve is made lower than the thresholdpressure of valve closing, and the valve is opened by righting moment ofspring 302. By repeating the above steps, the hydrogen flow through thevalve can be controlled.

As described above, the hydrogen delivery can be controlled by detectingthe valve opening state, and repeating heating of LaNi₅ according to thevalve opening state. In such a manner, the power generation section isprotected from damage by abrupt rise of, hydrogen generation pressure bymalfunction of the heater, and the activation of the heater can bestopped until the hydrogen generation pressure decreases to theprescribed pressure. In particular, in miniature fuel cells, the fuelshould be precisely fed with a simple structure. This Example shows theeffectiveness of the present invention.

1. A fluid delivery device having a valve for controlling a flow of afluid, comprising a flow channel for the fluid, and a valve in the flowchannel, wherein the valve operates in accordance with a pressuredifference between the upstream side and downstream side of the valvecaused by the flow of the fluid through the flow channel, allowing thefluid to flow when the pressure difference is lower than a prescribedvalue P₀, and intercepting the fluid not to flow when the pressuredifference is P₀ or more.
 2. The fluid delivery device according toclaim 1, wherein the valve is provided with an elastic body for takingat a prescribed position of the valve.
 3. The fluid delivery deviceaccording to claim 1, wherein the valve allows the fluid to flow throughthe flow channel in a prescribed direction, whereas the valve allows thefluid to flow in a direction reverse to the prescribed direction whenthe pressure difference lower than a prescribed pressure P₀ butintercepts the fluid not to flow when the pressure difference is P₀ ormore.
 4. The fluid delivery device according to claim 1, wherein thedevice comprises a first flow channel for delivery of the fluid, and asecond flow channel and a third flow channel branched from the firstflow channel, and the second flow channel is provided with the valve,the third flow channel is connected to a fluid element for analysis ofthe fluid, wherein the fluid is delivered from the first flow channel tothe second flow channel when the pressure difference is lower than P₀,and the fluid is delivered from the first flow channel to the third flowchannel when the pressure difference is not lower than P₀.
 5. The fluiddelivery device according to claim 4, wherein resistance to the flow inthe third flow channel is higher than resistance to the flow in thesecond flow channel when the valve is open.
 6. The fluid delivery deviceaccording to claim 5, wherein the fluid element is a column of liquidchromatography.
 7. The fluid delivery device according to claim 6,wherein the column for liquid chromatography is provided for analysis ofa chemical substance contained in the fluid.
 8. The fluid deliverydevice according to claim 6, wherein the column for liquidchromatography is a column for analysis of a protein contained in thefluid.
 9. The fluid delivery device according to claim 4, wherein thefluid element is a column of liquid chromatography.
 10. The fluiddelivery device according to claim 9, wherein the column for liquidchromatography is a column for analysis of a chemical substancecontained in the fluid.
 11. The fluid delivery device according to claim9, wherein the column for liquid chromatography is a column for analysisof a protein contained in the fluid.
 12. The fluid delivery deviceaccording to claim 1, wherein the flow channel is constituted of fourflow channels and an intersection thereof, a first valve being providedin one of the four flow channels and a second valve is provided onanother one of the four flow channels; the first valve allowing thefluid to flow toward the intersection, and the second valve operates inaccordance with a pressure difference between the upstream side anddownstream side of the valve caused by the flow of the fluid, allowingthe fluid to flow when the pressure difference lower than a prescribedpressure P₀, and intercepting the fluid not to flow when the pressuredifference is P₀ or more.
 13. The fluid delivery device according toclaim 12, wherein the device is further provided with a fluid elementfor analysis of the fluid, and the fluid in the intersection isdelivered to the fluid element when the pressure difference is not lowerthan P₀.
 14. The fluid delivery device according to claim 1, wherein thevalve has a movable electrode provided on a movable part capable ofbeing actuated by the pressure difference, a fixed electrode provided inopposition to the movable electrode, and a detection means for detectingelectrostatic capacity between the movable electrode and the fixedelectrode; and the flow of the fluid is controlled according to thedetected electrostatic capacity.
 15. The fluid delivery device accordingto claim 1, wherein the valve has a movable electrode provided on amovable part capable of being actuated by the pressure difference, afixed electrode provided in opposition to the movable electrode, and adetection means for detecting contact of the movable electrode with thefixed electrode; and the flow of the fluid is controlled by thedetecting means.
 16. A fuel cell having a fuel storing section forstoring a fuel, a power generating section for generating electric powerby use of the fuel, and a valve provided between the fuel storingsection and the power generating section, wherein the valve operates inaccordance with a pressure difference between the upstream side anddownstream side of the valve caused by the flow of the fluid through theflow channel, allowing the fluid to flow when the pressure difference islower than a prescribed pressure P₀, and intercepting the fluid not toflow when the pressure difference is P₀ or more.